1. Field of the Invention
This invention relates to methods and apparatus for temperature control in premises such as domestic dwellings and the like, using conduit-carried liquid or gaseous coolant for transferring heat energy. More particularly, the invention concerns a flowing coolant system using indoor heat exchangers which are thermally coupled to building structural elements such as tile or stone floors or radiators or finned tubing, wherein sensors and a controller are provided for establishing the dew point of the air in the building and for regulating the liquid coolant to maintain a surface temperature slightly above the dew point so as to prevent condensation on the indoor heat exchange elements.
2. Prior Art
In a building heating system it is necessary to transfer, to the indoor air in the building, heat energy developed by some form of heat collection device. In a building cooling system heat energy is extracted from the indoor air for transfer to a heat sink. A difference in temperature is needed between the heat exchange surfaces and the building air in order to effect thermal transfer. For heating, the heat exchanger is maintained at a higher temperature than the air, and remains dry. For cooling, however, the heat exchange surface is at a lower temperature than the air. Depending on the temperature of the heat exchanger and the dew point of the air, the heat exchanger may accumulate condensation from water vapor in the air.
In modern building systems the source or sink of heat energy is frequently associated with a heat pump. The heat pump employs two heat exchangers coupled in a circulating coolant loop, with a compressor and an expander disposed between the heat exchangers on opposite legs of the circulating loop, whereby heat energy is extracted at a cold side heat exchanger and transferred to a hot side heat exchanger. The indoor heat exchanger is maintained at a different temperature than the indoor air and the outdoor heat exchanger at a different temperature than the outdoor air or other means for providing or sinking heat energy.
Heat pumps can be used for either heating or cooling. The heat pump can be coupled to the building in a switchable manner for selecting whether the indoor heat exchanger will be the hotter or cooler of the two heat exchangers, for heating and cooling respectively. Air conditioning (cooling) apparatus virtually always use a heat pump, and insofar as heating systems use a heat pump, the output typically is supplemented by an additional heat source such as an electrical resistance heater or a furnace for burning natural gas or the like.
Whether heating or cooling, the heat pump system operates substantially in the same manner. However the direction in which the heat pump operates to transfer heat is reversed between the two modes. In either direction the movement of heat energy ca be considered a thermal energy transfer or load. There are a variety of means by which the thermal energy of the heat pump can be transferred to the air in the building; however, it is ultimately necessary to couple the system to one or more heat exchanging surfaces in actual contact with the building air, and to maintain the heat exchanging surface at a different temperature than the air for effecting thermal transfer.
In many installations the building air is passed through an indoor heat exchanger via forced air means. Typically, in the cooling mode, a fan is closely associated with a heat exchanger having a densely packed configuration of thermally conductive pipes with metal fins, through which a cold liquid refrigerant is circulated, exposed to interior air blown over the heat exchanger by the fan. This method is effective for transferring heat energy and the heat exchanger portion of the system is compact. On the other hand, in a forced air system the building must be provided with two sets of air ducts leading from the centralized heat exchanger to the air in the rooms to be heated or cooled, for supply and return of building air. The air ducts required can be quite large, especially for those sections of the supply and return ducts which are closest to the indoor heat exchanger in the typical branching pattern of ducts. The ducts are mounted insofar as possible between studs or other structural members of the building, but they inevitably occupy some of the space in the building which could be applied to occupant use.
One means for avoiding the need for large air ducts is to decentralize the indoor heat exchanger configuration. A liquid coolant circulation system allows circulation and transfer of thermal energy using coolant pipes, which are much smaller than air ducts. This arrangement is characteristic of heating systems using boilers. The liquid coolant, typically water, is heated at a central location and a circulating pump moves the hot water to a plurality of water-to-air heat exchangers located in the rooms to be heated. These heat exchangers are typically mounted along the baseboards of the building slightly above the floor and have a plurality of thermally conductive metal fins coupled to a metal conduit carrying the water or other coolant. Air currents for passing the building air over a typical baseboard heat exchanger are produced by convection rather than by a fan.
It is known in connection with hot water systems to more directly couple a hot water system to a structural element of a building in a so-called hydronic heating system. For example, ceramic tile, stone or concrete floors can be installed over a pattern of pipes for carrying heated water pumped from a boiler or from an intermediate heat exchanger coupled to the boiler, whereby the floor is warmed. The building air is warmed by contact with the floor. The floor surface area in such an installation is large as compared to the area of a typical baseboard heat exchanger, but the thermal transfer characteristics of tile or stone are poor as compared to metal. Additionally, the horizontal position of the floor is not optimal for producing convection currents. Therefore, floor heating via thermal transfer liquid is generally a heat source provided for comfort rather than for providing the basic mechanism whereby the thermal energy of a heating plant is coupled to the building air. Such a hydronic heat system is typically more comfortable than a forced air system because the interior air is not as dry, and the frequent need for a humidifier, with a heated forced air system, is eliminated.
The foregoing discussion of baseboard water circulation and embedded heat exchange pipe patterns relates to heating. It is possible to envision baseboard heat exchangers or an embedded pattern of pipes coupled to a thermal sink, for cooling a space. However, there is a major drawback to such a system. When the temperature of the surface of the floor or the like is lowered to the dew point of the air in the room, condensation accumulates on the heat exchange surfaces. In view of the need to cool a substantial volume of air using the circulating coolant, the coolant is normally provided at a temperature substantially lower than room temperature, almost certainly below the dew point of the air in the room. Condensation is thus a problem, and renders known systems of this type unsuitable for cooling floors and inconvenient for application to baseboard heat exchangers. It is advantageous to have a cool floor on a hot day, as well as cool air, but it is totally unacceptable to have a wet floor under any circumstances. Similarly, it may be possible to use baseboard heat exchangers for cooling, but it is inconvenient and impractical to provide a baseboard cooling system wherein every room includes a means for collecting and disposing of water condensed from the building air. In contrast, a forced air system has a single centralized heat exchanger for cooling, and condensation can be conveniently collected and disposed of centrally, typically by means of a gravity drain or by means of a condensate pump to a drain. Therefore, embedded pipe arrangements and baseboard heat exchangers are preferred only for heating and forced air means are typically provided for cooling, requiring two individual and separate systems to accomplish both heating and cooling.
It would be advantageous to provide a hydronic (water based) arrangement of heat exchangers and embedded pipes which would be useful to cool a space as well as to heat a space. In such an arrangement, the need for air supply and return ducts would be reduced or even eliminated.
Heat pump systems which include a cooling function are often provided with air heat exchangers inside the building and outside the building. It is also known to provide a ground source heat exchanger on the outside of the building, as a sole thermal source/sink or as a supplement to one or more other thermal transfer arrangements such as air heat exchangers. U.S. Pat. Nos. 5,054,541 - Tripp; 5,025,634 - Dressler; 4,753,285 - Rawlings; 4,058,982 - Wright, and others disclose ground source heat pump arrangements wherein certain of the problems with circulation and equilibrium of buried heat transfer loops have been addressed. Commonly owned application Ser. No. 725,962, filed Jul. 5, 1991, discloses a particularly convenient and efficient method and apparatus for installing a ground heat exchanger in a backhoe trench, at a relatively shallow position in the ground, for taking advantage of the stable underground temperature and heat supply or sink characteristics of the earth. These disclosures are hereby incorporated for their teachings of ground based heat exchange systems and ground mounted heat exchangers. However, as aforesaid, conventional air to air heat pump systems can also be utilized for operation of the subject invention, and are included within the scope of the subject invention.